U.S. patent application number 12/551926 was filed with the patent office on 2011-03-03 for writing data on alternating magnetic and nonmagnetic stripes of a servo pattern.
This patent application is currently assigned to SEAGATE TECHNOLOGY LLC. Invention is credited to SUNDEEP CHAUHAN, DAVID SHIAO-MIN KUO, MUSTAFA CAN OZTURK, PUSKAL PRASAD POKHAREL, ALEXEI H. SACKS, BARMESHWAR WIKRAMADITYA.
Application Number | 20110051286 12/551926 |
Document ID | / |
Family ID | 43624563 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110051286 |
Kind Code |
A1 |
POKHAREL; PUSKAL PRASAD ; et
al. |
March 3, 2011 |
WRITING DATA ON ALTERNATING MAGNETIC AND NONMAGNETIC STRIPES OF A
SERVO PATTERN
Abstract
A recordable magnetic media includes a servo pattern having a
plurality of adjacent alternating magnetic and nonmagnetic material
stripes. At least some of the magnetic material stripes have
magnetic transitions that define encoded data.
Inventors: |
POKHAREL; PUSKAL PRASAD;
(BLOOMINGTON, MN) ; OZTURK; MUSTAFA CAN;
(BLOOMINGTON, MN) ; WIKRAMADITYA; BARMESHWAR;
(EDEN PRAIRIE, MN) ; SACKS; ALEXEI H.; (EDINA,
MN) ; CHAUHAN; SUNDEEP; (FREMONT, CA) ; KUO;
DAVID SHIAO-MIN; (PALO ALTO, CA) |
Assignee: |
SEAGATE TECHNOLOGY LLC
SCOTTS VALLEY
CA
|
Family ID: |
43624563 |
Appl. No.: |
12/551926 |
Filed: |
September 1, 2009 |
Current U.S.
Class: |
360/131 ;
G9B/5.289 |
Current CPC
Class: |
G11B 5/855 20130101;
B82Y 10/00 20130101; G11B 5/743 20130101; G11B 5/82 20130101; G11B
5/59688 20130101 |
Class at
Publication: |
360/131 ;
G9B/5.289 |
International
Class: |
G11B 5/74 20060101
G11B005/74 |
Claims
1. A recordable magnetic media comprising: a servo pattern having a
plurality of adjacent alternating magnetic and nonmagnetic material
stripes, at least some of the magnetic material stripes having
magnetic transitions that define encoded data.
2. The recordable magnetic media of claim 1, wherein the magnetic
transitions of the magnetic material stripes define encoded data
that characterize repeatable runout (RRO) for at least one adjacent
data track.
3. The recordable magnetic media of claim 1, further comprising a
plurality of data tracks each extending in a downtrack direction
and arranged adjacent to each other in a crosstrack direction,
wherein the magnetic and nonmagnetic material stripes alternate in
the downtrack direction.
4. The recordable magnetic media of claim 1, wherein: a plurality
of data bits are encoded in the magnetic transitions of the
magnetic material stripes; and each data bit is encoded across at
least an adjacent pair of the magnetic material stripes with one of
the nonmagnetic material stripes therebetween.
5. The recordable magnetic media of claim 4, wherein for the data
bits encoded on the magnetic material stripes, magnetic transitions
in each data bit are encoded to occur during the nonmagnetic
material stripes.
6. The recordable magnetic media of claim 4, wherein a downtrack
width of each encoded data bit is greater than a downtrack width of
one of the magnetic material stripes.
7. The recordable magnetic media of claim 4, wherein the
nonmagnetic material stripes each have a downtrack width that is
not greater than one quarter of a downtrack width of each encoded
data bit.
8. The recordable magnetic media of claim 1, further comprising a
plurality of magnetic material data tracks each extending in a
downtrack direction and arranged adjacent to each other in a
crosstrack direction, wherein the magnetic and nonmagnetic material
stripes extend in the downtrack direction and alternate in the
crosstrack direction, and at least some of the magnetic material
stripes having magnetic transitions that define the encoded
data.
9. The recordable magnetic media of claim 8, wherein a crosstrack
width of an adjacent pair of the magnetic and nonmagnetic material
stripes is not greater than a width of one of the magnetic material
data tracks.
10. The recordable magnetic media of claim 1, further comprising a
plurality of magnetic material data tracks each extending in a
downtrack direction and arranged adjacent to each other in a
crosstrack direction with a nonmagnetic material track between each
adjacent pair of the magnetic material data tracks, wherein a first
radial column of the magnetic and nonmagnetic material stripes
extends in the downtrack direction and alternates in the crosstrack
direction, a second radial column of the magnetic and nonmagnetic
material stripes extends between the first radial column and the
data tracks and alternates in the crosstrack direction, the
magnetic material stripes in the first and second radial columns
are offset relative to each other in the cross track direction, and
at least some of the magnetic material stripes of the first and
second radial columns have magnetic transitions that define the
encoded data.
11. The recordable magnetic media of claim 10, wherein: the
magnetic material stripes in the first and second columns are
offset relative to each other in the crosstrack direction a
distance that is at least equal to a width of one of the magnetic
material data tracks.
12. The recordable magnetic media of claim 10, wherein: a
crosstrack width of the magnetic material stripes in the first and
second columns is at least as great as twice a crosstrack width of
an adjacent pair of the magnetic material data tracks.
13. An apparatus comprising: a recordable magnetic media having a
servo pattern with a plurality of adjacent alternating magnetic and
nonmagnetic material stripes, at least some of the magnetic
material stripes having magnetic transitions that define encoded
data; and a data encoder circuit that encodes data and writes the
encoded data as magnetic transitions in the magnetic material
stripes.
14. The apparatus of claim 13, wherein: the magnetic and
nonmagnetic material stripes of the servo pattern alternate in a
downtrack direction, and the data encoder circuit writes each of
the encoded data bits across at least an adjacent pair of the
magnetic material stripes with one of the nonmagnetic material
stripes therebetween on the servo pattern.
15. The apparatus of claim 14, wherein: the data encoder circuit
encodes writes the encoded data bits so that magnetic transitions
in each data bit occur over the nonmagnetic material stripes.
16. The apparatus of claim 13, wherein: the data encoder circuit
writes the encoded data bits so that a downtrack width of each
encoded data bit is no less than a combined downtrack width of an
adjacent pair of magnetic and nonmagnetic material stripes.
17. The apparatus of claim 13, wherein: the data encoder circuit
writes the encoded data bits as magnetic transitions on one of a
plurality of magnetic material strips in either a first column or a
second column, the first column comprising magnetic and nonmagnetic
material stripes extending in a downtrack direction and alternating
in a crosstrack direction, the second column comprising magnetic
and nonmagnetic material stripes extending between the first column
and data tracks and alternating in the crosstrack direction, the
magnetic material stripes in the first and second columns being
offset relative to each other in the cross track direction.
18. A method comprising: providing a recordable magnetic media
including a servo pattern having a plurality of adjacent
alternating magnetic and nonmagnetic material stripes; and writing
encoded data through a read/write head onto the alternating
magnetic and nonmagnetic material stripes so that magnetic
transitions in each data bit occur on the nonmagnetic material
stripes.
19. The method of claim 18, further comprising: writing each
encoded data bit across at least a portion of both of two adjacent
magnetic material stripes with a nonmagnetic material stripe
therebetween.
20. The method of claim 18, wherein the encoded data written onto
the magnetic material stripes characterize repeatable runout (RRO)
for at least one adjacent data track.
Description
BACKGROUND
[0001] The present invention generally relates to data storage
media and devices, and more particularly to data storage devices
that utilize discrete track media.
[0002] As the areal density of magnetic disc drives increases, so
does the need for more precise head position control when track
following, especially in the presence of vibrations which can cause
repeatable and non-repeatable runout error in head positioning and
variation in disk speed. Insufficient precision in bead position
control can result in unacceptable track misregistration (TMR),
which may result in erasure of adjacent tracks during writing
and/or unacceptable noise during reading due to sensing of adjacent
tracks. In an attempt to improve TMR margin and recording signal to
noise ratio (SNR), some magnetic disk media are patterned to form
discrete data tracks, referred to as discrete track recording
(DTR). DTR disks typically have a series of concentric raised zones
(also known as hills, lands, elevations, etc.) for storing data and
recessed zones (also known as troughs, valleys, grooves, etc.) that
provide inter-track isolation to reduce noise.
SUMMARY
[0003] Servo data can be encoded across a servo pattern that
includes a plurality of adjacent alternating magnetic and
nonmagnetic material stripes.
[0004] In some embodiments, a recordable magnetic media includes a
servo pattern having a plurality of adjacent alternating magnetic
and nonmagnetic material stripes. At least some of the magnetic
material stripes have magnetic transitions that define encoded
data.
[0005] In some other embodiments, an apparatus includes a
recordable magnetic media and a data encoder circuit. The
recordable magnetic media has a servo pattern with a plurality of
adjacent alternating magnetic and nonmagnetic material stripes, at
least some of the magnetic material stripes having magnetic
transitions that define encoded data. The data encoder circuit
encodes data and writes the encoded data as magnetic transitions in
the magnetic material stripes.
[0006] In some other embodiments, a recordable magnetic media is
provided that includes a servo pattern having a plurality of
adjacent alternating magnetic and nonmagnetic material stripes.
Decoded data is written through a read/write head onto the
alternating magnetic and nonmagnetic material stripes so that
magnetic transitions in each data bit occur on the nonmagnetic
material stripes.
DESCRIPTION OF THE DRAWINGS
[0007] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrate certain
embodiments of the invention. In the drawings:
[0008] FIG. 1 illustrates a servo pattern having alternating
magnetic and nonmagnetic material stripes in a downtrack direction
and which have magnetic transitions that represent synchronously
written (relative to the magnetic and nonmagnetic material stripe
pattern) encoded data, such as repeatable runout data, in
accordance with some embodiments;
[0009] FIG. 2 illustrates a block diagram of disk drive electronics
that may read and write encoded data to the exemplary servo pattern
of FIG. 1 and control head positioning responsive to the servo
pattern in accordance with some embodiments;
[0010] FIG. 3 illustrates another servo pattern having alternating
magnetic and nonmagnetic material stripes in a downtrack direction
and which has magnetic transitions that represent asynchronously
written encoded data, such as repeatable runout data, in accordance
with some embodiments;
[0011] FIG. 4 illustrates another servo pattern with alternating
magnetic and nonmagnetic material stripes having more narrow
downtrack widths and which has magnetic transitions that represent
written encoded data, such as repeatable runout data, in accordance
with some embodiments;
[0012] FIG. 5 illustrates another servo pattern with alternating
magnetic and nonmagnetic material stripes in a crosstrack direction
and which has magnetic transitions that represent asynchronously
written encoded data, such as repeatable runout data, in accordance
with some embodiments;
[0013] FIG. 6 illustrates another servo pattern with first and
second downtrack adjacent radial columns of crosstrack alternating
magnetic and nonmagnetic material stripes, where at least some of
the magnetic material stripes have magnetic transitions that
represent asynchronously written encoded data, such as repeatable
runout data, in accordance with some embodiments;
[0014] FIG. 7 illustrates another servo pattern with first and
second downtrack adjacent radial columns of crosstrack alternating
magnetic and nonmagnetic material stripes, where at least some of
the magnetic material stripes have increased crosstrack widths
relative to the strips of FIG. 8 in accordance with some
embodiments; and
[0015] FIG. 8 illustrates exemplary fields and information that may
be included in a servo pattern in accordance with some
embodiments.
DETAILED DESCRIPTION
[0016] Various embodiments of the present invention will now be
described more fully hereinafter with reference to the accompanying
drawings. However, this invention should not be construed as
limited to the embodiments set forth herein. Rather, these
embodiments are provided so that this disclosure will be thorough
and complete, and will convey the scope of the invention to those
skilled in the art.
[0017] It will be understood that, as used herein, the term
"comprising" or "comprises" is open-ended, and includes one or more
stated elements, steps and/or functions without precluding one or
more unstated elements, steps and/or functions. As used herein, the
singular forms "a", "an" and "the" are intended to include the
plural forms as well, unless the context clearly indicates
otherwise. When an element is referred to as being "connected",
"coupled", or "adjacent" to another element, it can be directly
connected, coupled, or immediately adjacent to the other element or
intervening elements may be present therebetween. In contrast, when
an element is referred to as being "directly connected", "directly
coupled", or "immediately adjacent" to another element, there are
no intervening elements present therebetween. The term "and/or" and
"/" includes any and all combinations of one or more of the
associated listed items. In the drawings, the size and relative
sizes of regions may be exaggerated for clarity. Like numbers refer
to like elements throughout.
[0018] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
region/element/value could be termed a second region/element/value,
and, similarly, a second region/element/value could be termed a
first region/element/value without departing from the teachings of
the disclosure.
[0019] Some embodiments may be embodied in hardware and/or in
software (including firmware, resident software, micro-code, etc.).
Consequently, as used herein, the term "signal" may take the form
of a continuous waveform and/or discrete value(s), such as digital
value(s) in a memory or register. Furthermore, various embodiments
may take the form of a computer program product on a
computer-usable or computer-readable storage medium having
computer-usable or computer-readable program code embodied in the
medium that is executable by a processor to perform functionality
described herein. Accordingly, as used herein, the terms "circuit"
and "module" may take the form of digital circuitry, such as
computer-readable program code executed by a processor (e.g.,
general purpose microprocessor and/or digital signal processor),
and/or analog circuitry.
[0020] Embodiments are described below with reference to block
diagrams and operational flow charts. It is to be understood that
the functions/acts noted in the blocks may occur out of the order
noted in the operational illustrations. For example, two blocks
shown in succession may in fact be executed substantially
concurrently or the blocks may sometimes be executed in the reverse
order, depending upon the functionality/acts involved. Although
some of the diagrams include arrows on communication paths to show
a primary direction of communication, it is to be understood that
communication may occur in the opposite direction to the depicted
arrows.
[0021] Although various embodiments of the present invention are
described in the context of disk drives for purposes of
illustration and explanation only, the present invention is not
limited thereto. It is to be understood that the present invention
can be more broadly used for writing data on recordable magnetic
media. Accordingly, although a recordable magnetic media can
include a disk of the disk drive, it is not limited thereto and may
include tape or other types of media. Moreover, although various
embodiments are described in the context of discrete track
recording (DTR) disk patterns, the invention is not limited thereto
and can be more broadly used for other types of patterned media
including, without limitation, bit patterned media (BPM).
[0022] DTR techniques for patterning a disk can accurately form a
pattern of magnetic and nonmagnetic regions. The nonmagnetic
regions may be formed as physical grooves into the media that
isolate adjacent lands/plateaus of magnetic regions. As explained
above, DTR has been applied to increase isolation between data
tracks and has further been used to pattern most of the servo
fields in servo sectors, which may be DC-erased to encode the
corresponding servo information. However, some servo data, such as
repeatable runout (RRO), is not known at the time the disk is
manufactured and must, instead, be determined after assembly of a
disk stack or assembly of the disk drive. These servo data have
heretofore been recorded on continuous magnetic recording areas
within the servo sectors.
[0023] RRO may be caused by patterning errors or writing errors
that result in non-circular tracks (e.g., RRO), spindle runout,
disk surface warping due to clamping of the disk on the spindle,
etc. After assembly of disks on the disk spindle, the RRO can be
measured relative to the angular position of the disks. Data that
characterizes the RRO for a particular servo sector and associated
data tracks can be written onto an adjacent continuous magnetic
recording area within the servo sector.
[0024] Some embodiments of the present invention, may arise from
the present realization that continuous magnetic recording areas
can deleteriously affect the head fly height by, for example,
causing a large disturbance force on the head as the head air
bearing changes from what is created by the pattern of alternating
lands and grooves to what is created by the continuous magnetic
recording area. Additionally, forming continuous magnetic recording
areas within servo sectors may complicate the manufacture process
by, for example, making it more difficult to planarize the raised
and recessed DTR areas which are adjacent to the continuous
magnetic recording areas. Various embodiments of the present
invention may improve topographic and non-topographic aspects of
patterned media.
[0025] In accordance with various embodiments, such continuous
magnetic recording areas are broken-up into radial and/or
circumferential stripes, and data are coded and written thereon in
a manner that allows recovery of the data despite this change. In
some embodiments, a servo pattern includes a plurality of adjacent
alternating magnetic and nonmagnetic material stripes, and servo
data are stored as magnetic transitions on the magnetic stripes.
The magnetic material stripes may be formed from a magnetic metal
alloy, a metal oxide, and/or a nonmagnetic material that contains
magnetic particles that are configured to be selectively magnetized
to store data bits. The nonmagnetic stripes may be formed as
grooves that separate and isolate the adjacent lands (plateaus) of
magnetic material stripes. Alternatively or additionally, the
nonmagnetic material stripes may contain a dielectric material that
is planar with, or recessed below (e.g., grooves), an upper surface
of the magnetic material stripes.
[0026] In some further embodiments, each bit of the recorded data
is encoded across at least an adjacent pair of the magnetic stripes
with one of the nonmagnetic stripes therebetween. The magnetic
transitions in each data bit may be encoded to occur during the
nonmagnetic stripes, although such alignment is not required. In
this manner, the data bits may be wide bi-phase encoded, or encoded
with another encoding technique, to generate a readback signal,
when read, that is similar to what would be generated if the servo
data were instead recorded on a continuous recording area.
Consequently, the servo data may be read from the alternating
magnetic and nonmagnetic stripes and processed by a read channel
circuit that is configured to receive conventional servo data from
a continuous recording area.
[0027] These and various other embodiments are described below with
regard to FIGS. 1-8. In a first group of embodiments, the servo
data are encoded across a plurality of magnetic and nonmagnetic
stripes that alternate in a downtrack direction. In a second group
of embodiments, the servo data are encoded along a plurality of
magnetic stripes that alternate with nonmagnetic stripes in a
crosstrack direction.
[0028] FIG. 1 illustrates a portion of a servo pattern 100 that has
magnetic stripes 110 (crosshatched stripes) and nonmagnetic stripes
120 (non-crosshatched stripes) that extend in a crosstrack
direction (e.g. radially across a disk/tape) relative to adjacent
circumferentially extending data tracks, and that alternate in a
downtrack direction. The servo pattern 100 may be repeated in each
radially extending servo sector around a disk. FIG. 1 further
illustrates digital servo data and the corresponding waveform after
the data are encoded for writing in a downtrack direction on the
servo pattern 100. The digital servo data may characterize RRO that
can be used by a servo controller to position a head so as to
compensate for the RRO while the head operates to read/write data
on a data track.
[0029] FIG. 8 illustrates an embodiment of at least a portion of
servo information that may be recorded on the servo pattern 100 of
FIG. 1 and/or on other embodiments of servo patterns disclosed
herein. The servo information can include preamble bursts, servo
address Mark (SAM) data, gray code (GC) data, position bursts
(e.g., A, B, C, D position bursts), and RRO data that characterize
RRO for an adjacent data track. The SAM data, GC data, and/or RRO
data may be wide bi-phase encoded, or encoded using another
encoding technique, when written onto the servo pattern 100.
[0030] As explained above, after assembly of a disk on a disk
spindle, RRO of the servo pattern can be measured and the RRO data
for a particular servo sector and associated data tracks can be
written onto the servo pattern 100. Although other servo
information, such as the SAM data and GC data, can be known before
manufacture of the disk and may, therefore, be patterned onto the
disk during its manufacture, these or other types of servo
information may alternatively be written on the servo pattern 100
after manufacture of the disk and assembly onto a rotational
spindle. Accordingly, the RRO data, the SAM data, the GC data,
and/or other servo data may be written through a head onto the
servo pattern 100.
[0031] In the exemplary embodiment of FIG. 1, the digital servo
data include a "000110" bit pattern. A data encoder circuit in the
disk drive encodes the bit pattern to generate the illustrated
encoded data waveform which is written onto the servo pattern 100.
In accordance with some embodiments, each data bit is encoded and
written at four times the servo clock period (4T) so that each
encoded data bit is written with a majority of the high or low
levels of the waveform (thus the corresponding magnetic
polarizations) recorded on the magnetic stripes 110. Thus, the each
data bit may extend across at least an adjacent pair of magnetic
stripes 110 with one of the nonmagnetic stripes 120 therebetween.
Although each data bit is shown in FIG. 1 as being encoded across
two adjacent magnetic stripes 110, it is to be understood that each
data bit may be written across any plural number of the magnetic
stripes 110.
[0032] The encoded data waveform may be written in a synchronous
manner relative to the servo pattern 100. The encoded transitions
in each data bit may be timed to occur during the nonmagnetic
stripes 120 and, may preferably, be timed to occur at a center of
the nonmagnetic stripes 120. However, the transitions may occur
over the magnetic stripes 110. For example, referring to FIG. 1,
the transitions from low to high levels in the data waveform for
each of the four servo data bits "0" occur during four of the
nonmagnetic stripes 120. Similarly, the transitions from high to
low levels in the data waveform for each of the two servo data bits
"1" occur during two of the nonmagnetic stripes 120. Because the
rapid transitions from low to high levels and from high to low
levels in the data waveform occurs over the nonmagnetic stripes
120, the readback signal that is generated as a head reads the
servo pattern 100 is not subjected to noise from the
transitions.
[0033] The downtrack width "d" of the nonmagnetic stripes 120
should be minimized to increase data storage density on the disk.
The selection of a downtrack width "d" of the nonmagnetic stripes
120 may include a compromise between various constraints, such as
avoiding creating head fly height disturbances between data track
and servo track zones, facilitating planarization of the patterns
during disk manufacture, providing sufficient write
synchronization, and/or providing sufficient readback signal
integrity.
[0034] For example, for the exemplary embodiment of FIG. 1 the
downtrack width "d" of the nonmagnetic stripes 120 may be less than
or equal to one quarter of the downtrack width of each encoded data
bit. As the downtrack width "d" of the nonmagnetic stripes 120
approaches zero, the servo pattern 100 approaches a continuous
magnetic recording area. In contrast, when the downtrack width "d"
of the nonmagnetic stripes 120 is twice the servo clock rate (2T),
the magnetic stripes 110 and the nonmagnetic stripes 120 can have
the same downtrack width.
[0035] FIG. 2 is a block diagram of disk drive electronic circuits
30 which include a data controller 52, a servo controller 53, and a
read/write channel 54. Although two separate controllers 52 and 53
and a read/write channel 54 have been shown for purposes of
illustration and discussion, it is to be understood that their
functionality described herein may be integrated within a common
integrated circuit package or distributed among more than one
integrated circuit package. A head disk assembly can include a
plurality of data storage disks 12, an actuator arm 18 with a
plurality of read/write heads 20 (or other sensors) which are moved
radially across different data storage surfaces of the disk(s) 12
by an actuator motor (e.g., voice coil motor) 28, and a spindle
motor which rotates the disk(s) 12.
[0036] The read/write channel 54 can convert data between the
digital signals processed by the data controller 52 and the analog
signals conducted through the heads 20. The read/write channel 54
provides servo data that is read from servo sectors 60 on the disk
12 to the servo controller 53. The servo sectors 60 may include the
servo data shown in FIG. 8 and may include the servo pattern 100 of
FIG. 1 and/or other servo patterns disclosed herein. The read/write
channel 54 can include a data encoder 400, an amplifier 402, an AFE
filter 410, and a data decoder 412. The data encoder 400 may be
configured to encode servo data to generate an encoded data
waveform that is amplified by the amplifier 402 and written onto
the magnetic stripes of the servo pattern (e.g. servo pattern 100).
As explained above, the data encoder 400 may be synchronized to the
servo pattern 100 (e.g. via synchronization performed using the
preamble field of FIG. 8 in the servo sectors 60) so that the level
transitions in the encoded data waveform for each bit occur over
the nonmagnetic stripes 120 (e.g., over centers of the nonmagnetic
stripes 120).
[0037] The readback signal from the servo pattern is filtered by an
AFE filter 410 that filters "double peaking" or other distortions
caused by the servo data bits being recorded across the nonmagnetic
stripes 120. "Double peaking" refers to distortions in the readback
signal that may appear as ripples due to the presence of the
nonmagnetic stripes. In particular, if a nonmagnetic stripe is
around the middle of the negative or positive half cycle of the
readback signal, the distortion may appear as two small peaks in
that half cycle. The AFE filter 410 may be configured to have a
cutoff frequency that removes non-fundamental (e.g., second, third
and higher) harmonic content of the readback signal. The data
decoder 412 decodes the encoded data from the servo pattern. After
filtering by the AFE filter 410, the data decoder 412 may operate
in a conventional manner to decode the servo data bits.
[0038] FIG. 3 illustrates a portion of another servo pattern 500
that has magnetic material stripes 510 (crosshatched stripes) and
nonmagnetic material stripes 520 (non-crosshatched stripes) that
extend in a crosstrack direction (e.g. radially across a disk/tape)
and that alternate in a downtrack direction. The servo pattern 500
may be repeated in each radially extending servo sector 60 around
the disk 12. FIG. 3 further illustrates digital servo data and the
corresponding waveform after the data are encoded for writing in a
downtrack direction on the servo pattern 500. The digital servo
data may characterize RRO and be used by a servo controller 53 to
position the head 20 so as to compensate for RRO while the head 20
operates to read/write data on a data track 62. One difference
between FIGS. 1 and 3 is that the encoded data waveform is written
asynchronously to the data pattern 500. The level transitions in
each servo data bit do not necessarily occur near a center of a
nonmagnetic material stripe 520, and the nonmagnetic material
stripes 520 (e.g., groove) may occur anywhere in the recorded data
bit. The maximum allowed downtrack width "d" of the nonmagnetic
stripes 520 may be smaller than that for synchronous writing
because known parts of the servo bits will not be written due to
the existence of the nonmagnetic stripes 120. However, allowing
asynchronous writing of servo data on the servo pattern 500 relaxes
requirements on the read/write channel 54 because synchronization
to the servo pattern 500 is not required.
[0039] The readback signal from reading the servo pattern 500 of
FIG. 3 may have various distortions such as uneven duty cycle and
double peaking that is dependent upon the phase differences. These
distortions may reduce the energy of the first harmonic (servo
frequency) of the signal and introduce higher harmonics into the
readback signal. The AFE filter can reduce these distortions since
the cut-off frequency is set close to the servo frequency.
[0040] When the downtrack width is 0, the readback signal will have
a waveform that corresponds to that from a continuous magnetic
recording area. In contrast, when the downtrack widths are 0.5T or
1T, for example, the readback signal can have double peaking
distortion due to the presence of the nonmagnetic stripes occurring
in each servo data bit. As the downtrack width "d" increases, the
severity of the distortion increases.
[0041] An Analog Front End (AFE) filter can be used to filter the
analog readback signal. The AFE filter should be configured to
substantially remove the distortions due to the grooves
(nonmagnetic stripes) between the lands (magnetic stripes) by
having a cutoff frequency that removes the higher order harmonic
content of the readback signals. Accordingly, with a downtrack
width "d" as great as 0.5T for the nonmagnetic stripes, it is
believed that the associated readback signal may be properly
filtered and processed by a read/write channel of the disk drive to
enable proper detection and decoding of the servo data bits
recorded therein.
[0042] FIG. 4 illustrates another servo pattern 600 with
alternating magnetic material stripes 610 and nonmagnetic material
stripes 620 that have more narrow downtrack widths than the servo
pattern 100 of FIG. 1 and the servo pattern 500 of FIG. 3.
Referring to FIG. 4, the combined downtrack width of an adjacent
pair of magnetic and nonmagnetic stripes 610 and 620 is less than
the period of the encoded data waveform (servo bit length).
Accordingly, each encoded servo data bit is written over at least
two pairs of magnetic and nonmagnetic stripes 610 and 620 (e.g., a
sequence of magnetic, nonmagnetic, magnetic, and nonmagnetic
material stripes). The quality of the readback signal may improve
as the downtrack widths of the nonmagnetic stripes 620 decreases
and the associated servo pattern frequency increases relative to
the servo bit frequency. For example, the ripple frequency in the
readback signal due to the nonmagnetic stripes 620 will increase
and may therefore be more easily removed by the AFE filter 410. As
the downtrack widths of the magnetic and nonmagnetic stripes 610
and 620 are varied relative to the servo T, the cutoff frequency of
the AFE filter 410 can be tuned to remove the ripples (which may
have more ripples than just the double peaks of the patterns of
FIGS. 1 and 5) in the readback signal caused by the nonmagnetic
stripes 620. The write waveform is not required to be synchronous
to the pattern 500. After filtering by the AFE filter 410, the data
decoder 412 may operate in a conventional manner to decode the
servo data bits.
[0043] Although the servo pattern 600 has been illustrated in FIG.
4 with the downtrack widths of the magnetic stripes 610 and the
nonmagnetic material stripes 620 being equal, their widths may
instead be unequal. The encoded data waveform may be written
synchronously or asynchronously to the servo pattern 600.
[0044] FIG. 5 illustrates another servo pattern 700 with
alternating magnetic material stripes 710 (crosshatched stripes)
and nonmagnetic material stripes 720 (non-crosshatched stripes)
that extend in a downtrack direction and alternate in a crosstrack
direction. The magnetic stripes 710 have magnetic transitions that
are recorded therein that represent asynchronously written encoded
data, such as RRO data, in accordance with some embodiments.
[0045] Referring to FIG. 5, the RRO data of the servo pattern 700
are followed by magnetic material recordable data tracks 730 and
nonmagnetic material nonrecordable tracks 740 that alternate in the
crosstrack direction and extend in the downtrack direction. The
nonrecordable tracks 740 provide isolation between the data tracks
730. The encoded servo data waveform is written onto the magnetic
stripes 710. The servo data may be RRO data that characterize
repeatable runout of the downtrack adjacent data tracks 730.
Different RRO data may be recorded on different magnetic stripes
710 to provide different RRO values for different data tracks 730.
The RRO data would typically be written onto the magnetic stripes
710 after assembly of the manufactured disks onto a spindle, such
as after assembly of the disk drive.
[0046] As shown in the exemplary embodiment of FIG. 5, the
crosstrack width of an adjacent pair of the magnetic and
nonmagnetic stripes 710 and 720 may be equal to or less than a
width of one of the data tracks 730. The data tracks 730 may have
the same crosstrack width as the nonrecordable tracks 740, although
their widths are not limited thereto. The crosstrack width of the
nonmagnetic stripes 740 may be reduced down to a size that, for
example, still permits an acceptable isolation between the data
tracks 730 and provides sufficient magnetic land for data writing
and recovery. In contrast to the servo patterns 100, 500, and 600,
continuous magnetic recording areas are provided by the elongated
magnetic stripes 710 in the servo pattern 700 for recording the
encoded servo data waveform.
[0047] As explained above, RRO data that are recorded in servo
wedges can be used to control head positioning so as to compensate
for the determined RRO while reading and writing data thereto. RRO
data that are used to compensate for RRO while reading data may be
written aligned with the centerline of the data track. In contrast,
the RRO data that are used to compensate for RRO while writing data
may be written with varying offset distances from a centerline of
the data track accounting for the radial offset between the read
and write elements of the head 20 as it moves between inner and
outer diameters locations on the disk 12. In accordance with some
embodiments, a servo pattern includes radial columns of RRO data
followed by the associated data tracks.
[0048] FIG. 6 illustrates a servo pattern 800 with first and second
downtrack adjacent columns RRO1 and RRO2 of crosstrack alternating
magnetic material stripes 810 and nonmagnetic material stripes 820
that store servo data. The alternating magnetic stripes 810 and
nonmagnetic stripes 820 in the columns RRO1 and RRO2 are offset in
the crosstrack direction. The columns RRO1 and RRO2 of servo data
are followed by magnetic material recordable data tracks 830 and
nonmagnetic material nonrecordable tracks 840 that alternate in the
crosstrack direction and extend in the downtrack direction.
[0049] In some embodiments, the first column RRO1 may be used to
store Write RRO for specific head (MR) jog offsets, such as,
without limitation, a MR jog offset of least 0.25 to no more than
0.75 times the track width. The second column RRO2 may be used to
store Read RRO for all other MR jog offsets, and may also be used
to store Write RRO as well. Additional error recovery of the Write
RRO data may be obtained by writing the Write RRO data to the
magnetic stripes 810 in both of the first and second columns RRO1
and RRO2. This redundancy may be particularly beneficial when one
of the fields is written with the higher curvature field from the
writer element.
[0050] In some other embodiments, the same RRO data are written to
some of the magnetic stripes 810 in the columns RRO1 and RRO2. For
example, a write element of the head 20 may have about the same
crosstrack width as one of the recordable data tracks 830 so that
when servo data are written onto the servo pattern 800, the head 20
will properly write the servo data onto one magnetic stripe 810 in
column RRO1 or in the column RRO2. For example, when the write
element of the head 20 is aligned with a data track 830, which in
the illustrated configuration of FIG. 6 is aligned with the
magnetic stripes 810 of the column RRO2, the servo data are written
onto a magnetic material stripe 810 of the column RRO2 but are not
written onto the uptrack adjacent nonmagnetic material stripe 820
of the column RRO1. Alternatively, when the head 20 is aligned with
a nonmagnetic track 840 between the magnetic track 830, the servo
data are written onto a magnetic material stripe 810 of the column
RRO1 but are not written onto the downtrack adjacent nonmagnetic
material stripe 820 of the column RRO2.
[0051] Although the magnetic stripes 810 and nonmagnetic stripes
820 are shown in FIG. 6 as having the same crosstrack width, which
may be the same as the data tracks 830, their width is not limited
thereto and may be different relative to one another, but should
have some radial overlap, such as shown in FIG. 7.
[0052] FIG. 7 illustrates another servo pattern 900 with first and
second downtrack adjacent columns RRO1 and RRO2 of crosstrack
alternating magnetic material stripes 910 (crosshatched areas) and
nonmagnetic material stripes 920 (non-crosshatched areas). The
magnetic stripes 910 have increased crosstrack widths relative to
the magnetic stripes 810 of FIG. 6. In the non-limiting exemplary
configuration of the servo pattern 900 shown in FIG. 7, the
magnetic stripes 910 have a crosstrack width that is about equal to
a combined crosstrack width of an adjacent pair of recordable
magnetic data tracks 930 with a nonrecordable nonmagnetic track 940
therebetween, although the relative widths of the stripes 910, 920,
930, and 940 may be greater than or less than that shown in the
exemplary embodiment of FIG. 7.
[0053] The same or different servo track data may be written to the
magnetic stripes 910 in the first and second columns RRO1 and RRO2.
In one embodiment, it may be known that at specific fractional MR
offsets the data can be more reliably stored in the first column
RRO1 or in the second column RRO2 because that particular column
will have more surface area of a corresponding one of the magnetic
stripes 910 under the write element of the head. Accordingly, at a
particular radial location on the disk the disk drive can be
configured to write and read data in a predetermined one of the
RRO1 and RRO2 columns.
[0054] In another embodiment, although it is known that because of
fractional MR offsets the data can be more reliably stored in the
first or second column, the disk drive does not attempt to
determine which of the two columns would provide more accurate
storage. Instead, the disk drive attempts to write the data across
both of the RRO1 and RRO2 columns and, because of the radial offset
and overlap between the magnetic stripes 910 in the respective
columns, the data will be written successfully onto the magnetic
stripe 910 of at least one of the RRO1 and RRO2 columns. During
data readback, the servo firmware can attempt to read the data from
the magnetic stripes 910 of at least one of the RRO1 and RRO2
columns and make both readback data sets available to the servo
controller which can pick one or the other or a combination thereof
after error correction and recovery. Although such redundancy can
result in a loss of storage capacity corresponding, the first or
second field may also be used to store other information, such as
fly-height detection related information, etc.
[0055] In yet another embodiment, the Write RRO data may be stored
in the magnetic stripes 910 in the first column RRO1, and both
Write RRO data and Read RRO data may be stored in the magnetic
stripes 910 in the second column RRO2. The downtrack width of the
first column RRO1 may be more narrow than the downtrack width of
the second column RRO2, such as when the RRO1 is configured to
store only Write RRO data and RRO2 is configured to stored both
Write RRO data and Read RRO data. The relative geometries of the
fields in the first and second columns may be defined as a function
of the writer width and the data storage land (magnetic stripes
910) widths.
[0056] In the drawings and specification, there have been disclosed
typical preferred embodiments of the invention and, although
specific terms are employed, they are used in a generic and
descriptive sense only and not for purposes of limitation, the
scope of the invention being set forth in the following claims.
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